Memory provides data storage for electronic systems. Flash memory is one of various memory types, which has numerous uses in modern computers and devices. A typical flash memory may comprise a memory array that includes a large number of non-volatile memory cells arranged in row and column fashion. The cells may usually be grouped into blocks. Each of the cells within a block may be electrically programmed by charging a floating gate. The charge may be removed from the floating gate by a block erase operation. Data may be stored in a cell as charge in the floating gate. NAND memory array may comprise a basic architecture of flash memory.
In recent years, vertical memory, such as three-dimensional (3D) memory has been developed. A 3D flash memory (e.g., 3D NAND memory array) device may include a plurality of strings of charge storage devices (memory cells) stacked over one another (e.g., in a first of three dimensions of 3D) with each charge storage device corresponding to one of multiple tiers of the device. The charge storage devices of a respective string may share a common channel region, such as one formed in a respective pillar of semiconductor material (e.g., polysilicon) about which the string of charge storage devices may be formed.
In a second dimension, each first group of the plurality of strings may comprise, for example, a group of strings sharing a plurality of access lines, known as wordlines (WLs). Each of the plurality of access lines may couple (e.g., electrically or otherwise operably connect) the charge storage devices (memory cells) corresponding to a respective tier of the plurality of tiers of each string. The charge storage devices coupled by the same access line (and thus corresponding to the same tier) may be logically grouped into memory pages, when each charge storage device comprises a multi-level cell capable of storing two bits of information.
In a third dimension, each group of the plurality of strings may comprise a group of strings coupled by corresponding data lines, known as bitlines (BLs). During operation of a computing device, data stored in the memory may be subjected to periodic (e.g., continuous) manipulations. These manipulations may be caused by internal control mechanisms, directed, for example, to optimize memory capacity, location areas, speed of access to memory, and the like. For example, the data may be moved from one area of memory to another area, copied from one area to another area, and the like. Accordingly, time to internally access data stored in a memory unit (e.g., memory block) may become an important factor in overall speed of manipulation of the data in the memory. For example, the lower the access time to a memory block, the lower is the time for an operation related to internal data manipulation.